This invention relates generally to gas pressure diaphragm regulator valves and particularly to gas pressure diaphragm regulator valves that include pressure relief mechanisms.
Gas pressure regulator valves are well known in the art. In such valves, a valve disc and a mating seat assembly are positioned intermediate an upstream and a downstream portion of a flowpath for controlling downstream pressure and flow by varying the valve opening, that is, the amount by which the valve disc is displaced from its valve seat. Pressure and flow regulation are achieved by modulating the valve opening to develop the downstream pressure required to deliver the flow demanded by the load. A popular form of regulating valve includes a diaphragm that acts as both a measuring and a loading device with the downstream pressure being applied to one side of the diaphragm against the forces of an opposed adjustable spring. The upstream pressure applies an opening force against the valve disc, which force is applied through a stem and linkage mechanism to a pusher post that is in communication with the diaphragm and the regulator spring. The downstream pressure applies an opposing force, i.e., one that tends to close the valve, to the diaphragm itself. The linkage mechanism has a mechanical disadvantage that enables the downstream pressure to offset the force of the regulator spring, thereby enabling regulation.
Valves of this type often incorporate a pitot tube for applying the pressure at the vena contracta, to the diaphragm. At the vena contracta, which is generally located a short distance downstream of the actual valve opening, the flow velocity is at a peak and the pressure is at a minimum. As those skilled in the art recognize, the so-called "droop", that is the drop in downstream pressure that occurs with increased load flow, may be offset by a number of techniques. In regulator valves with proportional control, droop is always present. The technique of velocity boosting is therefore frequently used, since it is simple, inexpensive and relatively effective. Velocity boosting essentially applies the lower pressure at the vena contracta, by means of a pitot tube, to the diaphragm rather than the higher controlled pressure downstream, with well-known improvements in operating characteristics of the regulator.
In a pipeline installation, there is always the possibility of a sudden increase in pressure that can pose significant problems for the regulating mechanisms coupled to the line. In a pressure relief diaphragm type regulator, means are provided for applying an increased pressure to the diaphragm to cause rapid closure of the valve orifice and protect the load equipment connected to the downstream side. While in many installations the regulating valves are not "pressure relieved", and some other mechanism is placed in the pipeline to protect against abnormal pressure increases, the present invention is only concerned with pressure relief type diaphragm valves. Under an excess pressure condition, the regulating valve can be damaged or even destroyed by the abnormally large force applied to the diaphragm. As discussed in copending application Ser. No. 054.297, even in a pressure relief type diaphragm regulator the linkage may be stressed to the point of damage or destruction. Although the pusher post, retainer and pressure relief indicator of that invention are disclosed herein, they form no part of the present invention.
In a pressure relief type diaphragm regulator valve, provision must be made for rapidly enabling a large increase in downstream pressure to be communicated to the diaphragm to quickly close the valve. In a regulator valve utilizing velocity boosting, the long narrow pitot tube and the small registration orifice pose a significant impediment to pressure relief operation since the size of the passageway communicating between the downstream side of the casting body, where the valve is located, and the lower chamber, where the diaphragm is located, is quite small. Consequently, it is difficult, if not impossible, to apply the high pressure to the diaphragm rapidly enough to effectuate valve closing to protect downstream loads connected to the pipeline.
With the present invention, a velocity boost body with a wrap-around pitot tube is provided for sampling the pressure at the vena contracta through a small registration orifice. The boost body is configured to enable a large passageway to be established between the downstream side of the body casting and the diaphragm under an excess pressure condition.